The present invention relates to liquid-supply tanks wherein a liquid is maintained in the tank beneath an air cushion which is under pressure for the purpose of not only maintaining a relatively constant pressure on the liquid but also equalizing pressure variations which might otherwise occur.
In particular, the present invention relates to a system for rapidly building up the air cushion over the liquid in the tank under conditions where the latter is initially installed or is being set up for operation after inspection, repair, or the like.
Moreover, the present invention relates to a system according to which the air cushion once it is established is maintained over the liquid in the liquid-supply tank.
Associated with the liquid-supply tank is an air-supply tank which communicates with the liquid-supply tank for maintaining the air cushion therein during normal operation. Flow of liquid between these tanks is controlled by a valve such as a pressure-responsive valve which responds to pressure in the liquid-supply tank.
Methods and apparatus of the above type are already known, for example, in the form of compressors which are utilized for the initial buildup and maintaining of the air cushion over the liquid in the liquid-supply tank. However, such conventional arrangements are disadvantageous in that the installations are expensive and subject to frequent faulty operation.
There are other known methods and apparatus of the above type where instead of a compressor there is provided an air-supply tank connected in parallel with the liquid-supply tank with suitable control valves being provided so that with such an arrangement also it is possible to maintain a given air cushion over the liquid in the liquid-supply tank. However, arrangements of this latter type are exceedingly disadvantageous in that in order to initially build up the air cushion, an extremely long time is required because the volumetric efficiency of such installations is extremely low.